Spectroscopic characterization of iron-containing MCM-58

Fe(III) species were introduced into the zeolite MCM-58 by two different methods, namely by the addition of ferric nitrate to the synthesis gel (FeMCM-58) and by ion exchange of the calcined (Al)MCM-58 material with ferric chloride (Fe-MCM-58). The materials were characterized by XRD, SEM, AAS, UV–Vis, EPR and 27Al and 29Si MAS NMR spectroscopy. The studies indicate the presence of framework substituted Fe(III), isolated Fe(III) and iron oxide clusters in the FeMCM-58 materials. Further NO adsorption studies were carried out with dehydrated FeMCM-58 and Fe-MCM-58 and studied by EPR at two different frequencies (X- and Q-band at 77 K and 6 K, respectively) to investigate the possible reduction of the introduced Fe(III) ions. The studies show that the dehydration process resulted in the formation of Fe(II) species by autoreduction of isolated Fe(III) species in both materials, which in turn were involved in the formation of a paramagnetic high spin Fe(II)–NO complex as the major species. Hence our studies confirm the presence of isolated Fe(III) species not only in the Fe-MCM-58 material, but also in the calcined FeMCM-58 materials.